Synthetic gaseous fuels have been produced for many years. The early processes were based on using heavy oils or coal in relatively low pressure cyclic thermal-operations which produced a gas of about 500 BTU/SCF. These processes disappeared from the United States with the advent of the natural gas production and transmission industry.
They also became uneconomical in other countries in the early 50's when the availability of low cost naphtha led to the commercial development of catalytic reforming of naphtha for the production of 500 BTU Town Gas.
Since the basic catalytic naphtha reforming process produces a lean gas high in hydrogen and carbon oxides and low in methane, considerable effort was expended to develop suitable process modifications to produce a gas high in methane so as to avoid the need for enriching with light hydrocarbons. These efforts successfully culminated in the development of the so called rich gas processes. Ultimately, catalytic naphtha reforming demonstrated a capability of producing a high BTU gas which was essentially all methane.
Aside from the limitations imposed by the required use of premium and ever-increasing high cost feed stocks such as naphtha, the main disadvantage of catalytic processes for the production of substitute natural gas is the requirement for operating at conditions very close to regions where carbon forms. The catalyst must be maintained in an active state to favor rapid formation of gaseous hydrocarbons. If the rate of reaction is reduced, tar formation and carbon producing reactions become competitors and result in catalyst degradation. These conditions require frequent changeover of the catalyst, often at most inopportune times.
Catalyst poisons such as sulfur, as well as high operating temperatures, also cause a loss of catalytic activity and the inevitable formation of carbon. Once carbon is formed and deposited on the catalyst, it catalyzes its own continued production, ultimately leading to loss of plant production.